Blatant self-promotion but my company released https://crates.io/crates/mysql-proxy built on tokio-core (the current crate of the week). It’s a lightweight and scalable proxy where you can easily plug in your own proxy logic to handle packets.

I think an obvious choice is ripgrep. It’s a phenomenal piece of work, and is an actually useful program. This isn’t to slight the work others have done on the crates in this list, but ripgrep is something that people who have no interest in Rust itself can actually get and use. It’s something we can hold up and say “see, you totally can write useful software in Rust; it isn’t just for PL research wanking!”

The one mitigating aspect would be that I’m not sure, at this point, whether ripgrep needs any more publicity than it’s already gotten.

I nominate llvm_build_utils which allows for stable usage of LLVM bitcode from your Rust code. I found this while working on u128/i128 shim (now accepted as another RFC, though). It might actually be easier to write than assembly if what you really want is an intrinsic or just finer-grained signal to the LLVM optimizer—it has significant potential in my humble opinion.